Process of purifying molybdenite concentrates



Patented Apr. 15, 1941 PROCESS OF PURIFYING MOLYBDEN ITE CONCENTRATESCharles H. Curtis, Miami, Aria, assignor to Miami Copper Company, NewYork, N. Y., a corporation of Delaware No Drawing. Application May 26,1939, Serial No. 275,843

14 Claims.

The present invention relates to a process of purifying molybdeniteconcentrates, or molybdenite-bearing materials, and more particularly toa process of obtaining molybdenite concentrates substantially free fromdeleterious im- 5 contaminants due to the natural limitations of thephysical concentration processes. The amount and nature of thesecontaminants had a direct bearing on the commercial value of theseconcentrates. Copper, even when present in relatively small amounts, hasbeen found to be particularly deleterious and undesirable, as isreflected in the price structure. Thus the sales price at a recent dateof molybdenite concentrates containing about 2.5% copper was 33 perpound of contained MoSz, but was 45 per pound for concentratescontaining less than about 0.3% copper. The physical separation andrejection of the copper bearing mineral, or minerals, by the so-calledphysical processes was usually only partially complete, and obtained atthe expense of reduced recoveries of the molybdenite. Furthermore, thereusually were considerable variations in the degree of completeness ofthese physical separations, which resulted in varying grades ofconcentrate and varying over-all recovery of the molybdenite. Suchvariations were, of course, economically disadvantageous.

I have discovered a process which makes it feasible to avoid thelimitations of the physical concentration processes when applied to theproduction of the desired very high grade commerical molybdeniteconcentrate, in that physical concentration of the ores or other sourceof molybdenum sulfide need be carried only so far as to produce apreliminary concentrate representing the best economic balance of gradeand recovery obtainable by the physical concentration. By the process ofthe present invention, a

molybdenite concentrate, e. g., such a preliminary concentrate, issubjected to a special chemic altreatment to produce a final commercialmolybdenite concentrate containing substantially no copper.

It is an object of the present invention to provide a process forpurifying molybdenite concenimpurities such as copper sulfide with smallor inappreciable loss of molybdenum sulfide.

A further object of the present invention is the provision of a processfor purifying molybdenite concentrates'by freeing them fromobjectionable impurities, particularly copper sulfide, which process maybe carried out commercially and on an industrial scale.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the following detailed description ofthe invention.

Generally speaking, the process of the present invention is a chemicalone whereby the copper, in particular, and other contaminants renderedsoluble, are dissolved without an appreciable loss of molybdenum. Thischemical process differs fundamentally from the physical concentrationprocesses in that it is more positive; the completeness of the removalof the copper being under direct control and entirely independent of themolybdenite recovery. In practicing the present process, the specificand selective chemical dissolution of the copper and other contaminantsrendered soluble is accomplished without dissolving an appreciableamount of molybdenite.

The process of the present invention comprises bringing an agentcontaining a compound selected from the group consisting of manganesedioxide and manganese dioxide yielding materials, either separately orjointly, into contact with the molybdenite concentrates in the presenceof strong mineral acid in dilute form, such as sulfuric acid,hydrochloric acid and mixtures thereof. The chemical reaction, orreactions, thus set up are greatly accelerated by increased temperature,making it desirable to carry them on at, or near, the boiling point ofthe solution. The liquid portion of the mixture containing the copperand other components, thus dissolved, can then be separated from theinsoluble residue containing the undissolved molybdenite by any of themethods familiar to those skilled in the art, such as, filtration andwashing, or by decantation and washing. In this manner, molybdenumsulfide concentrates initially containing deleterious amounts ofimpurities, including copper sulfide, are satisfactorily purified andsubstantially freed from copper with negligible losses of molybdenumsulfide.

For the purpose of giving those skilled in the art a betterunderstanding of the present invention. the following specific examplesare given as illustrative of the mode of carrying out the presentinvention and of the results obtained from practicing the presentinvention. The invention contemplates the use of manganese dioxideyielding materials which contain small amounts of iron, as well as thematerials set forth in examples herein given to illustrate theinvention.

Example N o. I

A molybdenite concentrate assaying about 89.3% molybdenum sulfide (M082)and about 0.96% copper (Cu) was pulped with water to approximately 50%solids and mixed with manganese dioxide (MnOz) and sulfuric acid (H2804)in approximately the following ratios:

Pounds per ton MoSz concentrates MnOz (89.3% MnOz) 56 H2SO4 (100% H2804)160 The mixture was heated to approximately 200 F. and the reactionallowed to proceed for about 4 hours. After separating the solution fromthe insoluble material by filtration and washing, the

latter assayed approximately 92.7% M032 and only about 0.14% copper. Therecovery of molybdenum sulfide was about 99.94% of the originalmolybdenum sulfide and about 85.5% of the copper had been removed.

Example No. II

A second quantity of the same concentrate used in Example No. I wassimilarly treated with manganese-iron ore and sulfuric acid inapproximately the following ratios:

Pounds per ton MoSz concentrate a ManganeseIron ore (38% Mn, 12% Fe,

chiefly oxides) '70 H2804 (100% H2804) 270 A molybdenite concentrateassaying about 83.2% molybdenum sulfide (M082) and about 4.5% copper(Cu) was similarly treated with manganese dioxide (MnOz) and sulfuricacid (H2604) in approximately the following ratios:

Pounds per ton MOSz concentrates MnOz (89.3% MnOz) 300* H2804 (100%H2804) 550 The leached material which was separated from the solutionafter about 4 hours at a temperature of about 200 F., assayed about88.5% molybdenum sulfide (M0532) and about 0.29% copper. The recovery ofthe original molybdenum sulfide was about 99.81% and about 93.5% of theoriginal copper wasremoved.

Example No. I V

A second sample of the same concentrate used in Example No. III wassimilarly treated with manganese-iron ore and sulfuric acid inapproximately the following amounts:

Pounds per ton M0S2 concentrates Manganeseiron ore (38% Mn, 12% Fe,

chieflyas oxide) 496 H2SO4 (100% H2804) 6.20

After thoroughly mixing the materials, the mixture was maintained atabout 200 F. for about 4 hours. The insoluble material recovered afterseparating the soluble constituents therefrom assayed about 83.8%molybdenum sulfide (Moss) was added in commercial concentration.

with varying grades of concentrates.

and about 0.26% copper. About 95.1% of the original copper was removedand about 99.9% of the original molybdenum sulfide (M082) recovered.

Example No. V

From a molybdenite concentrate assaying about 75.9% molybdenum sulfide(MOSz) and about 1% copper (Cu), two samples were subjected to identicaltreatments except that hydrochloric acid (HCl) was added to one andsulphuric acid (H2SO4) to the other. Each sample was pulped with waterto about 50% solids and manganese-iron ore of the type described inExamples Nos. II and IV added in a ratio of about '70 pounds per ton ofM052 concentrate. To one sample was added about 268 pounds of H01 and tothe other about 360 pounds of H2804 per ton of concentrate. It will benoted that the two amounts of acid are approximately chemicallyequivalent. After heating the mixtures and recovering the insolublematerial in the same manner as previous examples, the insoluble materialassayed about 0.025% copper where HCl had been used and about 0.35%copper where H2SO4 had been used. In each case less than 0.05% of theMOSz was dissolved.

The generally higher cost of hydrochloric acid makes it economicallyadvantageous to use sulfuric acid in mose cases. However, it will beobserved that hydrochloric acid was actually metallurgically superior tosulfuric acid in this instance and might under certain conditions beused in preference to sulfuric acid.

In the foreging examples the acid, although computed on the basis ofI-IzSOr or I-ICl, It should be understood that the acid may be added inany desired concentration. Similarly the amount of water used to pulpthe concentrate is not critical and may vary from the amounts used inthe foregoing specific examples. However, it is clear that throughcontrol of the amount of water, not only can the bulk of pulp to behandled be held at a minimum, but also a control over the chemicalconcentrations of the leach solution can be exercised independent of theamount of reagents added.

The amounts of compound or agent, other than acid, required are more orless dependent primarily upon the impurity content of the molybdeniteconcentrates, and consequently will vary It will be understood thatvariations in the amount and nature of contaminants that are renderedsoluble in addition to the copper contained in the-concentrates willcause variations in the ultimate amount of reagents required. For thisreason it is not practicable to give a general definition of the amountsof reagents to be added in terms of the copper content alone. As thoseskilled in the art will readily understand, the amount of reagentsrequired for treating any particular concentrate may be readilydetermined in the light of the foregoing description by preliminarypilot tests and/or a chemical analysis thereof. I have found itadvantageous for the purpose of control of the leach to observe thechemical nature of the leach solution during the progress of the leachand have noted when iron is present in the solution that the degree ofoxidation of the iron in solution as indicated by the amount of ferriciron present in the solution after the reactions are substantiallycomplete is oftentimes an excellent guide to the completeness of thecopper removal. I have observed, for exampla that a ferric iron contentof from four to ten pounds per ton of solution in the final leachsolution, or an amount of ferric iron equal to approximately ten totwenty per cent of the total iron in solution, commonly accompaniessatisfactory dissolution of the copper. I have, therefore, found itconvenient to control the addition of the agent containing the compoundselected from the group Consisting of manganese dioxide and manganesedioxide yielding materials by the concentration of ferric iron, ordegree of oxidation of the iron in the final leach solution. The mostfavorable ferric iron concentration may vary according to the nature ofthe contaminating minerals in the particular molybdenite concentratesbeing treated, as one skilled in the art Will readily understand. Itwill also be understood that the iron in solution is derived fromdissolution of iron bearing minerals in the concentrates as well as fromthe compound or agent added when that compound contains iron renderedsoluble in the course of the reactions. 7

The acid requirements vary according to the reagent or reagents used inconjunction with it. I have found that the final acid concentration ofthe leaching solution: i. e., the excess acid remaining after thereaction or reactions are substantially complete, is a satisfactoryguide to the acid addition. For example, in leaches involving manganesedioxide and sulfuric acid I have found a satisfactory final acidconcentration to be about 4 to 7% by weight of the liquid portion.

When hydrochloric acid is used, the conditions are similar to thosedescribed for sulfuric acid,

i. e. final acid concentrations of from about 4 to about 7% by weight ofthe liquid portion have been found satisfactory.

If nitric acid is used, the acid concentration should be kept below acritical maximum of about 1.25%. The loss of molybdenite by dissolutionis greater where nitric acid is employed, but may be kept under about 3%provided the critical concentration is not exceeded. Generally speaking,sulphuric acid and hydrochloric acid are used in preference to nitricacid.

It will be seen from the foregoing illustrative examples that the strongmineral acid (such as sulphuric acid and hydrochloric acid), regardlessof the concentration in which it is added, is in dilute form in themixture during the course of the reactions due to the presence of thewater used to pulp the mass.

It is desired to make clear that there is no, limitation implied, orintended, in the foregoing disclosure as to the ultimate source of thespecific reagents involved. The term compound selected from the groupconsisting of manganese dioxide and manganese dioxide yielding materialsnot containing more than a small amount of iron is used in thespecification and the claims to denote these reagents singly and incombination.

It will be understood that the above illustrative examples are oiferedmerely as an aid in the exposition of my invention and that nolimitations are imposed on said invention by reason thereof. It will berecognized by those skilled in the art that it might be desirable todeviate from the above specifications according to the individualconditions which might prevail in the application of the invention, butthat such deviation, or deviations, would not depart from the spirit ofthe invention.

From the foregoing it will be observed that the process of the presentinvention accomplishes the removal of deleterious impurities,particularly copper sulfide, in a very satisfactory manner withinappreciable loss of the valuable molybdenum sulfide. The process isrelatively inexpensive and lends itself to commercial application on anindustrial scale.

Although the present invention has been described in connection withcertain specific and illustrative embodiments thereof, it will beunderstood by those skilled inthe art that variations and modificationsthereof may be made without departing from the spirit and scope of thepresent invention as defined by the appended claims.

I claim:

1. The process of treating molybdenite concentrates to remove coppercompounds, including copper sulphide without appreciable loss ofmolybdenite comprising pulping molybdenite concentrates with water,mixing said pulped concentrate with sulphuric acid and with a compoundselected from the group consisting of manganese dioxide and manganesedioxide yielding materials, said manganese dioxide yielding materialsnot containing more than a small amount of iron, heating the mixture forabout 4 hours at a temperature of about 200 F. and separating the liquidportion containing the soluble constituents from the insoluble residuewhereby a molybdenite concentrate substantially free from coppercompounds including copper sulphide is obtained without an appreciableloss of molybdenite by dissolution.

2. The process of treating molybdenite concentrates to remove coppercompounds, including copper sulphide without appreciable loss ofmolybdenite comprising pulping molybdenite concentrates with water,mixing said pulped concentrate with hydrochloric acid and with acompound selected from the group consisting of manganese dioxide andmanganese dioxide yielding materials, said manganese dioxide yieldingmaterials not containing more than a small amount of iron, heating themixture for about 4 hours at a temperature of about 200 F. and

separating the liquid portion containing the soluble constituents fromthe insoluble residue whereby a molybdenite concentrate substantiallyfree from copper compounds including copper sulphide is obtained withoutan appreciable loss of molybdenite by dissolution.

3. The process of treating molybdenite concentrates to remove coppercompounds, including copper sulphide without appreciable loss ofmolybdenite comprising pulping molybdenite concentrate with water,mixing said pulped concentrate with strong mineral acid and with acompound selected from the group consisting of manganese dioxide andmanganese dioxide yielding materials, said manganese dioxide yieldingmaterials not containing more than a small amount of iron, heating themixture for about 4 hours at a temperature of about 200 F., andseparating the liquid portion containing the soluble constituents fromthe insoluble residue whereby a molybdenite concentrate substantial- 1yfree from copper compounds including copper sulphide is obtained withoutan appreciable loss of molybdenite by dissolution.

4. The process of treating molybdenite bearing materials includingmolybdenite concentrates to remove undesirable impurities includingcopper sulphide comprising treating said materials with dilute sulphuricacid in the presence of manganese dioxide containing not more than asmall amount of iron, heating the mass at an elevated temperature untilthe reactions are substantially complete and separating the liquidportion containing the soluble constituents from the insoluble residuewhereby a molybdenite concentrate relatively free from undesirableimpurities including copper sulphide is obtained Without an appreciableloss of molybdenite.

5. The process of treating molybdenum bearing materials includingmolybdenite concentrates to remove undesirable impurities includingcopper sulphide comprising treating said materials with dilutehydrochloric acid in the presence of manganese dioxide containing notmore than a small amount of iron, heating the mass at an elevatedtemperature until the reactions are substantially complete andseparating the liquid portion containing the soluble constituents fromthe insoluble residue whereby a molybdenite concentrate relatively freefrom undesirable impurities including copper sulphide is obtainedwithout an appreciable loss of molybdenite.

6. The process of treating molybdenite bearing materials includingmolybdenite concentrates to remove undesirable impurities includingcopper sulphide comprising treating said materials with a strong mineralacid in dilute form in the presence of a compound selected from thegroup consisting of manganese dioxide and manganese dioxide yieldingmaterials, said manganese dioxide yielding materials not containing morethan a small amount of iron, heating the mass at an elevated temperatureuntil the reactions are substantially complete and separating the liquidportion containing the soluble constituents I from the insoluble residuewhereby a molybdenite concentrate relatively free from undesirableimpurities including copper sulphide is obtained Without an appreciableloss of molybdenite.

7. The process of removing copper sulphide from molybdenite bearingmaterials including molybdenite concentrate without an appreciable lossof molybdenite comprising treating the materials with a hot dilutesolution of a strong mineral acid and a compound selected from the groupconsisting of manganese dioxide and material containing predominantamounts of manganese dioxide and containing not more than a small amountof iron and thereafter separating the liquid reaction products from theconcentrate to free it substantially from copper compounds.

8. The process of removing copper sulphide from molybdenite bearingmaterial without an appreciable loss of molybdenite comprisingtransforming the copper sulphide to a compound soluble in Water bytreating the material with strong mineral acid in dilute form and with acompound selected from the group consisting of manganese dioxide andmanganese dioxide yielding materials, said manganese dioxide yieldingmaterials not containing more than a small amount of iron, and washingout the soluble copper compound.

9. The process of removing copper sulphide from molybdenite bearingmaterial without an appreciable loss of molybdenite comprisingtransiorining the copper sulphide to a compound soluble in water bytreating the material with manganese dioxide containing not more than asmall amount of iron and strong mineral acid in dilute form, andseparating the liquid reaction products from the insoluble residue.

10.The process as set forth in claim 9 in which the strong mineral acidis sulphuric acid.

11. The process as set forth in claim 9 in which the strong mineral acidis hydrochloric acid.

12. The process of removing copper sulphide from molybdenite bearingmaterial without an appreciable loss of molybdenite comprisingtransforming the copper sulphide to a compound soluble in water bytreating the material with manganese ore containing not more than asmall amount of iron and strong mineral acid in dilute form, andseparating the liquid reaction products from the insoluble residue.

13. The process as set forth in claim 12 in which the strong mineralacid is sulphuric acid.

14. The process as set forth in claim 12 in which the strong mineralacid is hydrochloric acid.

CHARLES H. CURTIS.

